Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $224.87   10.212%   $247.8337   $247.83   $247.85   $247.80  
  Purchase #2 $164.72   13.491%   $186.9424   $186.94   $186.95   $186.90  
  Purchase #3 $225.28   11.237%   $250.5947   $250.59   $250.60   $250.60  
  Purchase #4 $215.69   9.581%   $236.3553   $236.36   $236.35   $236.40  
  Purchase #5 $46.46   6.533%   $49.4952   $49.50   $49.50   $49.50  
  Purchase #6 $178.97   7.200%   $191.8558   $191.86   $191.85   $191.90  
  Purchase #7 $64.82   5.252%   $68.2243   $68.22   $68.20   $68.20  
  7 purchase totals = $1,120.81       $1,231.3014   $1,231.30   $1,231.30   $1,231.30